1. Technical Field
The present invention relates to an image scanning apparatus incorporated in, for example, a copier, a facsimile apparatus or a copier-facsimile system, and more particularly to an image scanning apparatus which can effectively determine whether a lamp of a light source of the image scanning apparatus is functioning appropriately.
2. Background Art
A certain type of copier-facsimile system includes not only a flat bed scanner (FBS) for scanning one sheet of an original document at a time by placing the original document on a scanning table but also an automatic document feeder (ADF) for successively scanning a plurality of documents by stacking the documents on a paper feed tray.
When the document is scanned by the flat bed scanner, the document is stationarily placed on the scanning table. With the document being fixed by a cover placed over the document, a light source and a plurality of mirrors of a scanning unit are moved under the scanning table upon actuation of an associated motor. The scanning unit moves from a scanning start position under a front end of the scanning table to a scanning end position under a rear end of the scanning table. A light is being radiated to the document from the light source through the scanning table while the scanning unit is moving, and a reflected light is scanned by an image pick-up element such as CCD via the mirrors and lens. CCD outputs black and white binary image data according to the scanned image.
On the other hand, the automatic document feeder successively feeds the documents over the scanner automatically from the paper feed tray. The scanner is not moved during scanning. An image on each document is scanned by CCD when it passes over a translucent plate. A mirror is positioned just below the translucent plate so that CCD can obtain the image reflected by this mirror.
Before scanning the document by the flat bed scanner, a lamp checking is performed to the light source of the scanning unit every time a user presses a start key. The lamp checking is scanning of a white plate. As illustrated in FIG. 7 of the accompanying drawings, which schematically indicates a scanning bed 31 and a white plate 43a' as viewed from the top, the white plate 43a' is located at a position P5 next to the flat bed 31 in a sub-scanning direction or outside a scanning start position P3 of the scanner. The lamp testing is necessary because brightness or luminance of the light source eventually drops below an appropriate value due to aging or the like. Scanning of the white plate is self diagnosis or examination conducted before scanning. Data relating to one line of the document scanned is converted to binary data, and if there are white pixels more than a predetermined value (e.g., 90%), it is determined that the lamp of the light source emits an appropriate light an good condition. Then, the document scanning is initiated. When a plurality of documents are scanned using the automatic document feeder, another white plate placed above the translucent plate (not shown in FIG. 7) is scanned to examine the lamp of the light source. Therefore, the image scanning apparatus which includes both the flat bed scanner and the automatic document feeder has two white plates for lamp testing.
Since one of the white plates 43a' is located beyond the scanning start position P3 of the scanner or outside a scanning table area but inside the image scanning apparatus in the subscanning direction of the scanner (or direction in which a carriage supporting the light source moves), the length of the scanning apparatus in the sub-scanning direction is elongated by at least the length of the white plate 43a'. Thus, it is difficult to reduce the size of the scanning apparatus. In addition, since two white plates are required, the number of components is large and construction of the apparatus is complicated. Moreover, the carriage first has to move to the lamp check position P5, which is next to the scanning start position P3 in a direction opposite to the scanning direction of the scanner (the scanner moves from the scanning start position P3 to a scanning end position P4 or from the FBS front end to the FBS rear end in FIG. 7) every time a sheet of document is scanned by the flat bed scanner. Accordingly, a user must wait for a while after pressing a start key until the scanning really starts.